The diesel engine manufacturer can provide design data concerning the rate of heat rejection from the engine jacket, lubricant cooler and from the turbocharger aftercooler.. The followin
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Section 3: INFORMATION REQUIRED FOR DESIGN
3.1 Introduction This section defines the data that must be developed to establish engineering design bases and to evaluate between various design and ownership alternatives
3.2 Electrical Loads Electric loads should be determined carefully to size electric generating plant components properly The duration and
variation of electric loads should be determined to provide inputs to
required life-cycle cost analyses and for various clauses when tailoring NAVFAC guide specifications, (refer to Section 1) for procurement purposes 3.2.1 Electric Load Determination To determine the electric load that the plant must satisfy, utilize the load estimating data described in NAVFAC DM-4.01, Electrical Engineering, Preliminary Design Considerations For retrofit projects, the local utility may be able to supply load duration curves from actual metering records
3.2.2 Typical Electrical Load Curves Figure 1 is an example of a typical electrical load curve
3.2.2.1 Growth Curve In Figure 1(a), note the normal trend of growth in electric demands and the additional loads (steps) when new buildings or processes are added Development of this data and preparation of the growth curve is useful in timing additions to power plant generating capacity 3.2.2.2 Average 24-Hour Load Curves The average of daily electrical
demands in Figure 1(b), showing 24-hour variation in seasonal demands, is very important Such curves are useful in determining load factors, the duration of certain demands, and in dividing the total electric load among plant units This information is a necessary factor in life-cycle cost analyses to be conducted when selecting among alternative designs and
equipment configurations
3.2.2.3 Annual Load Durations Curves Plot the duration in hours, of each load during a year for both present and future load conditions The type of curve shown in Figure 1(c) is useful in determining load factors and in sizing electric generating plant equipment Information from this curve is also used in required life-cycle cost analyses Durations of plant electric loads at full load, three-quarters load, and at one-half load is a required input for tailoring NAVFAC guide specifications
3.3 Duty and Capacity Requirements for Electric Generating Plants Sources and duty types of electric generating plants are defined in Section 2
Table 2 summarizes capacity requirements as related to each duty type
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3.6.1.4 Rotational Speed The maximum allowable rotational speed in
revolutions per minute (rpm) for the duty and generator set capacity desired
should be indicated in accordance with applicable criteria
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3.6.4 Cooling Systems
3.6.4.1 Cooling Medium Record whether the cooling fluid is water or a mixture including water and an additive Specify the additive and provide the mixture concentration in percent
3.6.4.2 Cooling Water Enter the flow rate of cooling water needed to cool the engine in gallons per minute (gpm) Also record the leaving water
temperature and the temperature rise allowed for the engine These
parameters may be obtained from the diesel engine manufacturer
3.6.4.3 Heat Rejection The diesel engine manufacturer can provide design data concerning the rate of heat rejection from the engine jacket, lubricant cooler and from the turbocharger aftercooler
3.6.5 Generator Room
3.6.5.1 Heat Radiated from the Engine and the Generator The engine
manufacturer can supply the rate at which heat is radiated from the engine
A value of 7 percent may be used until more refined information is
developed Consider that most large generators have an efficiency of at least 96 percent Utilize a 4 percent value of the generator's kilowatt rating converted to Btu's for the heat radiated from the generator For smaller units increase the percent as appropriate
3.6.5.2 Design Ambient Temperatures The outdoor design temperature for ventilation of the generator room is found in NAVFAC P-89, Engineering
Weather Data Refer to applicable criteria to determine the inside design temperature and maximum allowable temperature rise Outdoor dry and wet bulb design temperatures will be required for the selection of cooling
towers and air conditioned spaces, and dry bulb temperatures for the
selection of radiator type engine cooling
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Section 4: COGENERATION CONSIDERATIONS
4.1 Introduction Cogeneration is the simultaneous on-site generation of electric energy and process steam or heat from the same plant Use of heat recovery can increase overall efficiency of diesel-electric generation from around 33 percent, which is available for most diesel engine-generators, to
a theoretical 75 percent Heat which would otherwise be wasted is recovered for use in building heating, ventilating and air conditioning systems and,
in special cases, to generate additional power Process thermal loads can also be served where practicable Guidelines for assessing the potential for cogeneration, the circumstances when it should be considered, and
discussions on the types of equipment to utilize are addressed in the
following paragraphs
4.2 Design Considerations Cogeneration applications should be considered for all new designs of prime duty diesel-electric generating plants
Cogeneration may be considered for existing plants if proven economically viable Standby/emergency plants will rarely justify use of cogeneration, although in some cases heat recovery systems may be economical Packaged cogeneration units may be considered for stand-alone installations; however, the system and components must comply with the applicable criteria
4.2.1 Fuel Availability Fuel availability should be assured for the life
of the project
4.2.2 Load Sizing Criteria The following criteria shall be used in the design of cogeneration installations:
4.2.2.1 Electric and Thermal Loads Electric and thermal loads should be continuous to satisfy economic criteria Only limited fluctuations in
thermal loads are permitted unless adequate thermal storage systems or
standby boilers are provided
4.2.2.2 Load Balance The electric load should be in reasonable balance with both the heating peak and average load The ratio of peak to average load for cogeneration installations should be in the range from 2:1 to 3:1 4.2.2.3 Load Coincidence Time and quantity demands for electric power and thermal energy should have a coincidence of not less than 70 percent
Coincidence is defined as the ratio of the maximum coincident total demand
of a group of loads to the sum of the maximum demands of individual loads comprising the group, both taken at the same point of supply at the same time
4.2.3 Prime Mover Sizing Size the cogeneration prime mover for heat
recovery equivalent to 50 to 75 percent of the maximum thermal load
4.2.4 Thermal Product Properties Design cogeneration installations
producing steam and/or hot water as thermal products and to provide these products at the same pressures and temperatures as existing distribution 15
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4.2.5 Power Sales Agreements Power sales agreements made with utility companies shall be in the "Surplus Sales" category wherein only the power generated in excess of facility demand is sold to the utility Design of the facility and negotiation of the power sales agreement should reflect Navy policy which is to reduce utility costs rather than to seek profits from the private sector for cogenerating Other arrangements are possible where all the electric power generated is sold to the utility at a price based on the utility's highest unit cost of generation and is purchased back from the utility at a cost lower than that at which it was sold These types of arrangements should be explored for commercial ownership options as covered in Section 2
4.2.6 Site Adaptability Building, site, and facility utility systems must
be compatible with adaptation required to accommodate cogeneration
equipment Adequate space must be available For large plants, a minimum
of 5,000 sq ft (465 sq m) to 7,000 sq ft (650 sq m) should be allocated in preliminary planning stages
4.2.7 Electric Utility Grid Interconnection
4.2.7.1 United States Locations The local utility must allow cogenerators
to interconnect with their supply grid
4.2.7.2 Foreign Locations Situations in foreign locations must be
determined individually Where such interconnections are not allowed, it may be possible to isolate various loads for a dedicated cogeneration
facility
4.2.8 Grid Protection Requirements Grid protection/interconnection
equipment and ownership requirements vary depending on the Power Sales
Agreement negotiated with the utility The local utility should be
contacted very early in the design concept stage because requirements differ significantly Utility companies may provide assistance in planning
facilities
4.3 Heat Recovery Applications Heat recovery is the process of extracting heat from the working medium or mediums, such as diesel engine exhaust
gases, and transferring this heat to a source of water, air, etc
4.3.1 Sources of Waste Heat Heat may be recovered from engine jacket and lubricant cooling systems and from the exhaust gases Table 6 indicates the potential for product heat recovery from each source Theoretically, all of the jacket and lubricant cooling water heat can be recovered; practically in most cases only about one-half will be reclaimed to provide useful work Although applications are limited, direct use of the exhaust gases for
product drying, etc., can increase overall efficiency about 12 percent
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Table 6
Summary Heat Balance: Cogeneration Using
Diesel-Engine Generators
ÚÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔ¿
³ Without Cogeneration With Cogeneration ³
³ (Percent of Fuel Input) ³
³ Item ÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔ´
³ Useful Useful Heat ³
³ Work Losses Work Recovered Losses ³ ÊÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔ´
³ ³
³ Diesel Engine/Generator 33 33 ³
³ Set ³
³ ³
³ Jacket and Lubricant ³
³ Cooling Waters 30 15 15 ³
³ ³
³ Exhaust Gas 30 12 18 ³
³ ³
³ Radiation Losses 7 7 ³
³ ³ ÊÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔ´
³ ³
³ Totals 33 67 33 27 40 ³
³ ³ ÊÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔ´
³ ³
³ Overall Efficiency 33 60 ³
³ ³ ĂÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔỖ 4.3.2 Design Priority The first responsibility of the jacket and
lubricant cooling system design shall be to cool the engine; heat recovery
equipment is of secondary importance Silencing the engine is also of
secondary importance unless the engine is located outside the building close
to a quiet zone, e.g., sleeping quarters All heat recovery installations
should provide alternate, conventional systems to reject heat from jacket
and lubricating oil cooling media (see Figure 2)
4.3.3 Heat Recovery from Jacket and Lubricant Cooling Systems
4.3.3.1 Hot Water Systems Recovery of waste heat from jacket coolant is
the preferred method of heat recovery Heat recovery from the lower
temperature and flow of lubricant coolant may also prove economically
justified Heat is recovered via heat exchangers to secondary loops (see
Figure 2) The engine coolant loop must be a closed system Recovery of
heat from lubricant oil coolers is accomplished in the same fashion These
hot water systems can be combined with an exhaust gas heat recovery boiler
into an integrated system
4.3.3.2 Steam Systems Jacket coolant leaving the engine is piped to a
heat recovery boiler The reduced pressure in the boiler and in piping to
the boiler allow jacket coolant to flash to low pressure steam Steam is
returned from process uses to the engine coolant inlet as condensate
Pressures must be controlled and engine cooling system must be carefully
designed to prevent boiling or flashing within the engine A static head
and controlled steam pressure system is preferred over a pressure-reducing
valve or an orifice at the boiler inlet
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